EP0910119B1 - Method for oxidizing a structure during the fabrication of a semiconductor device - Google Patents
Method for oxidizing a structure during the fabrication of a semiconductor device Download PDFInfo
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- EP0910119B1 EP0910119B1 EP98308341A EP98308341A EP0910119B1 EP 0910119 B1 EP0910119 B1 EP 0910119B1 EP 98308341 A EP98308341 A EP 98308341A EP 98308341 A EP98308341 A EP 98308341A EP 0910119 B1 EP0910119 B1 EP 0910119B1
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- 238000000034 method Methods 0.000 title claims description 26
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 239000004065 semiconductor Substances 0.000 title claims description 12
- 230000001590 oxidative effect Effects 0.000 title description 9
- 238000006243 chemical reaction Methods 0.000 claims description 21
- 239000003989 dielectric material Substances 0.000 claims description 10
- 150000004767 nitrides Chemical class 0.000 claims description 7
- 239000003990 capacitor Substances 0.000 claims description 6
- 239000000758 substrate Substances 0.000 claims description 5
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 claims description 4
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 claims description 2
- 229910052721 tungsten Inorganic materials 0.000 description 25
- 230000003647 oxidation Effects 0.000 description 24
- 238000007254 oxidation reaction Methods 0.000 description 24
- 239000010937 tungsten Substances 0.000 description 23
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 20
- 229910052751 metal Inorganic materials 0.000 description 14
- 239000002184 metal Substances 0.000 description 14
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 14
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 10
- 239000000463 material Substances 0.000 description 10
- 229920005591 polysilicon Polymers 0.000 description 10
- 229910052710 silicon Inorganic materials 0.000 description 9
- 239000010703 silicon Substances 0.000 description 9
- 239000007800 oxidant agent Substances 0.000 description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 239000007789 gas Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 239000003870 refractory metal Substances 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 239000003638 chemical reducing agent Substances 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 238000001020 plasma etching Methods 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- -1 preferably O2 Substances 0.000 description 4
- 239000010936 titanium Substances 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 229910021417 amorphous silicon Inorganic materials 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 229910001882 dioxygen Inorganic materials 0.000 description 2
- 229910021421 monocrystalline silicon Inorganic materials 0.000 description 2
- 238000000059 patterning Methods 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 229910008807 WSiN Inorganic materials 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000002360 explosive Substances 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000009877 rendering Methods 0.000 description 1
- 238000010405 reoxidation reaction Methods 0.000 description 1
- 229910021332 silicide Inorganic materials 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical group [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical group N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/60—Electrodes
- H01L28/82—Electrodes with an enlarged surface, e.g. formed by texturisation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/28008—Making conductor-insulator-semiconductor electrodes
- H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
- H01L21/28026—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor
- H01L21/28035—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor the final conductor layer next to the insulator being silicon, e.g. polysilicon, with or without impurities
- H01L21/28044—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor the final conductor layer next to the insulator being silicon, e.g. polysilicon, with or without impurities the conductor comprising at least another non-silicon conductive layer
- H01L21/28061—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor the final conductor layer next to the insulator being silicon, e.g. polysilicon, with or without impurities the conductor comprising at least another non-silicon conductive layer the conductor comprising a metal or metal silicide formed by deposition, e.g. sputter deposition, i.e. without a silicidation reaction
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
- H01L21/321—After treatment
- H01L21/32105—Oxidation of silicon-containing layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/60—Electrodes
- H01L28/82—Electrodes with an enlarged surface, e.g. formed by texturisation
- H01L28/90—Electrodes with an enlarged surface, e.g. formed by texturisation having vertical extensions
Definitions
- the present invention pertains to semiconductor devices, and more specifically, to a method for oxidizing or reoxidizing a structure during the fabrication of a semiconductor device.
- polycrystalline silicon used for these purposes in conventional processes has several limitations, due mainly to its higher resistivity.
- a thermal oxidation step is needed after the gate patterning, especially for memory devices.
- This oxidation step is needed to remove damage caused by the patterning and etching of the gate structure (primarily at the gate edges) by reactive ion etching (RIE) and to thicken the gate oxide on the edge so as to improve its reliability and reduce sharp corners at the lower edges of the conductive gate structure.
- RIE reactive ion etching
- this oxidation step may create problems because tungsten easily oxidizes at temperatures greater than around 350°C in an oxygen ambient.
- a solution to this problem involves using H 2 and H 2 O to oxidize any existing silicon or silicon oxide surfaces while leaving any tungsten surfaces unoxidized. See K. Nakajima, et al., Poly-metal Gate Process --- Ultrathin WSiN Barrier Layer Impermeable to Oxidant In-diffusion during Si Selective Oxidation, CONFERENCE PROCEEDINGS ULSI XI, 1996 MATERIALS RESEARCH SOCIETY 317-323 (1996 ).
- a problem with this approach is that a very small amount of water can be used and it is extremely difficult to controllably introduce such small amounts of water in large scale production of semiconductor devices.
- the selective oxidation method disclosed herein involves the oxidation of one material (M 1 ) without substantially oxidizing another material (M 2 ).
- the chemical reactions for the oxidation of M 1 and M 2 are (using O 2 as the oxidizer) : 2M 1 + O 2 ⁇ 2M 1 O + E 1 (1) 2M 2 + O 2 ⁇ 2M 2 O + E 2 (2) where E 1 and E 2 are the enthalpies of formation for reactions (1) and (2), respectively.
- a combination of an oxidizer, preferably O 2 , and a reducer, H 2 are utilized.
- the minimum requirement for the successful selective oxidation of M 1 while not appreciably oxidizing M 2 is that reaction (1) is favored as compared to reaction (2).
- E 1 is less than E 2 .
- M 1 represents silicon, polycrystalline silicon, or amorphous silicon and M 2 represents tungsten
- E 1 is less than E 2 (-911 kJ/mol versus -562 kJ/mol)
- the silicon of reaction (3) will oxidize much more readily than the tungsten of reaction (4).
- a method of fabricating a capacitor having a dielectric between a bottom electrode and a top electrode and situated over a semiconductor substrate comprises the steps of: providing the bottom electrode over the semiconductor substrate; providing an oxidizable dielectric material over the bottom electrode; and subjecting the bottom electrode and the oxidizable dielectric material to an explosive reaction between O 2 and H 2 in a semiconductor processing chamber, wherein the oxidizable dielectric material is oxidized and the bottom electrode remains substantially unoxidized, such that the reaction between the O 2 and H 2 does not increase the pressure in the processing chamber beyond a predetermined safe level.
- the dielectric material is, preferably, comprised of a material selected from the group consisting of: an oxide/nitride stack, BST, tantalum pentoxide, PZT, or any combination thereof.
- a method of oxidizing selective materials such as silicon (single crystal, polycrystalline, or amorphous silicon) without appreciably oxidizing any other materials (such as a tungsten or tungsten nitride structure) is disclosed herein.
- the oxidation is performed by introducing hydrogen gas and oxygen gas into a chamber where the semiconductor wafer resides and heating the wafer and/or the chamber. Note, however, that the introduction of hydrogen gas along with oxygen gas can be very volatile.
- the system pressure should not exceed its safety limit in the presence of the following reaction 2H 2 + O 2 ⁇ 2 H 2 O + E (5) where E is the enthalpy generated by this reaction.
- reaction (5) occurs as H 2 and O 2 are entered into the system, then the reaction occurs in only part of the volume of the chamber. By doing this, the safety of the process is improved and the process window can be enlarged because the reaction occurs in only a portion of the total volume of the process chamber thereby leaving the rest of the volume available for expansion. In this case, reaction (5) occurs continuously as the gases enter into the chamber instead of filling the entire chamber with the gases before ignition of the gases.
- a variation of this approach is to start the reaction at a lower pressure and increase the pressure once the reaction starts.
- Anther variation involves starting the reaction at a lower concentration of one gas (such as O 2 ) and increasing the concentration once the reaction starts.
- FIGUREs 1 and 2 illustrate a transistor formed using such a method.
- gate insulating layer 104 preferably an oxide layer -- more preferably SiO 2
- a semiconductive layer preferably insitu doped, exsitu doped, or undoped polysilicon
- a metal layer is formed (preferably deposited).
- the metal layer is comprised of a refractory metal (preferably tungsten, cobalt, aluminum, or titanium) formed over a nitride layer (preferably comprised of the refractory metal and nitrogen -- more preferably tungsten nitride).
- a nitride layer preferably comprised of silicon and nitride - more preferably Si 4 N 3 ).
- gate structure 120 preferably comprised of polysilicon structure 108, tungsten nitride structure 110, tungsten structure 112, and silicon nitride structure 114.
- this etch step is performed by reactive ion etch (RIE) but it can be accomplished using any standard processing step.
- RIE reactive ion etch
- One drawback to this etch step, especially when RIE is used, is that it may degrade the gate dielectric at locations 106. If left untreated, this may increase the leakage of the device or may lower the gate oxide integrity (GOI) thereby rendering the device non-functional or damaged.
- the damaged portions of gate insulating layer 104 are reoxided along with the oxidation of surfaces 116 of polysilicon structure 108 and surfaces 118 of metal structure 110 and 112. In fact, it may even entirely oxidize metal structures 110 and 112. This will severely degrade the device because the conductivity of the resulting structure (including layers 110 and 112) may greatly decrease due to the oxidation of the metal (especially where the metal is tungsten). Oxidation of metal structures 110 and 112 may also cause peeling.
- the method disclosed herein allows for the reoxidation of layer 104 and the oxidation of silicon-containing structure 108 while leaving metal structure 112 (preferably comprised of W, Ti, Co, Cu, or Al) and metal-nitride structure 110 (preferably comprised of a nitride and a refractory metal such as W, Ti, Co, Cu, or Al - more preferably tungsten nitride) substantially unoxidized.
- metal structure 112 preferably comprised of W, Ti, Co, Cu, or Al
- metal-nitride structure 110 preferably comprised of a nitride and a refractory metal such as W, Ti, Co, Cu, or Al - more preferably tungsten nitride
- this oxidation step is accomplished by providing around 12% O 2 and H 2 into a chamber in which the wafer is provided.
- the pressure within the chamber is preferably around 100 Torr and the temperature is around 1000°C.
- Using this embodiment for around 60 to 80 seconds (preferably 70 seconds) will result in around 3 nm of oxide to be formed on bare silicon and thin silicon oxide, and it will result in around 6 to 10 nm of oxide to be grown on polysilicon structures. While these specific conditions are preferred, the temperature, pressure, time, and amount of oxygen versus that of hydrogen can be changed so as to grow more or less of an oxide film so long as oxidation of the silicon or silicon oxide structure is accomplished while not substantially oxidizing the metal or metal nitride structures.
- This method of fabrication may be implemented to selectively oxidize silicon structures in the presence of tungsten under the following conditions: the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O 2 to H 2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours.
- the mixture of hydrogen and oxygen can be used to selectively oxidize a particular material (such as Ta 2 O 5 or BST) without oxidizing other materials which are present (such as copper, tungsten, platinum, or other refractory metal or conductive structure which may be used to make an electrode of a memory cell) in developing electronic devices (such as the memory cell of a DRAM).
- a particular material such as Ta 2 O 5 or BST
- other materials which are present such as copper, tungsten, platinum, or other refractory metal or conductive structure which may be used to make an electrode of a memory cell
- This particular selective oxidation method can be accomplished by using an O 2 and H 2 ambient to oxidize a capacitor dielectric. While this alternative method is preferably performed as a rapid thermal process step with relatively low ambient pressures, it can be implemented in many ways.
- An advantage of this method is that it may be implemented using a lower thermal budget (preferably, the temperatures required will be around 400 to 1000°C) and it can be used so as to oxidize the capacitor dielectric while leaving other features (such as tungsten, platinum, copper, or other similar materials) substantially unoxidized.
- this alternative method of fabrication may be implemented under the following conditions: the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O 2 to H 2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours.
- FIGURE 3 illustrates a memory cell which is fabricated using the method disclosed herein.
- the memory cell can be formed either over or under the bitline, and it may either be formed as a "crown cell” or as a planar cell and it may or may not be formed of rugged polysilicon or hemispherical grain polysilicon.
- the memory cell of FIGURE 3 is comprised of substrate 302, interlevel dielectric 304, conductive plug 306 (preferably comprised of doped single-crystal or polycrystalline silicon), bottom electrode base 310 and upright portions 312, dielectric layer 314 and top electrode 316. Basically, the method can be used to either form dielectric 314 and/or to prevent the oxidation of bottom electrode 310 and 312.
- conductive plug 306 and electrode 310 and 312 are formed of tungsten and if the dielectric material requires a high temperature anneal in an oxygen containing ambient (such as Ta 2 O5 and BST require), then the method disclosed may be utilized to prevent the oxidation of these features.
- the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O 2 to H 2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours.
- dielectric 314 is formed or reoxided by subjecting the wafer to a mixture of H 2 and O 2 .
- this is accomplished using the following conditions: the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O 2 to H 2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours.
- FIGURE 4 is a graph illustrating relative sheet resistivity of a tungsten layer which is approximately 60 nm thick and is subjected to the oxidation step of the method disclosed herein versus the percentage of O 2 /H 2 mixture.
- the pressure is around 100 Torr at around 1000°C.
- Points 402 and 404 illustrate that the sheet resistivity of a tungsten layer subjected to an oxidation step of the method disclosed herein, where the O 2 /H 2 mixture is 10% or less, has the same sheet resistivity as a tungsten layer which has not been subjected to an oxidation step.
- Point 406 illustrates that the sheet resistivity of a tungsten layer subjected to an oxidation step of the instant invention, where the O 2 /H 2 mixture is around 20%, has a sheet resistivity around 20% higher than that of an untreated tungsten layer.
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Description
- The present invention pertains to semiconductor devices, and more specifically, to a method for oxidizing or reoxidizing a structure during the fabrication of a semiconductor device.
- As device dimensions continue to decrease to achieve higher density and performance, there is an increasing demand for highly conductive gate structures, interconnects, and electrodes for metal on silicon (MOS) devices. The polycrystalline silicon ("poly" or "polysilicon") used for these purposes in conventional processes has several limitations, due mainly to its higher resistivity.
- Recently, various metal silicides have been considered because they have a conductivity which is higher than that of polysilicon by about an order of magnitude. However, future devices with very high integration densities will, most likely, need to be fabricated with higher conductivity materials for gate structures and interconnects. Therefore, either all metal structures will need to be formed or structures which are comprised of polysilicon and a refractory metal (such as tungsten, molybdenum, cobalt and/or titanium).
- With regards to the formation of a gate structure, a thermal oxidation step is needed after the gate patterning, especially for memory devices. This oxidation step is needed to remove damage caused by the patterning and etching of the gate structure (primarily at the gate edges) by reactive ion etching (RIE) and to thicken the gate oxide on the edge so as to improve its reliability and reduce sharp corners at the lower edges of the conductive gate structure. If a polysilicon and tungsten gate structure is used, this oxidation step may create problems because tungsten easily oxidizes at temperatures greater than around 350°C in an oxygen ambient.
- A solution to this problem involves using H2 and H2O to oxidize any existing silicon or silicon oxide surfaces while leaving any tungsten surfaces unoxidized. See K. Nakajima, et al., Poly-metal Gate Process --- Ultrathin WSiN Barrier Layer Impermeable to Oxidant In-diffusion during Si Selective Oxidation, CONFERENCE PROCEEDINGS ULSI XI, 1996 MATERIALS RESEARCH SOCIETY 317-323 (1996). A problem with this approach is that a very small amount of water can be used and it is extremely difficult to controllably introduce such small amounts of water in large scale production of semiconductor devices.
- The selective oxidation method disclosed herein involves the oxidation of one material (M1) without substantially oxidizing another material (M2). The chemical reactions for the oxidation of M1 and M2 are (using O2 as the oxidizer) :
2M1 + O2 → 2M1O + E1 (1)
2M2 + O2 → 2M2O + E2 (2)
where E1 and E2 are the enthalpies of formation for reactions (1) and (2), respectively. In order to achieve this selective oxidation, a combination of an oxidizer, preferably O2, and a reducer, H2, are utilized. The minimum requirement for the successful selective oxidation of M1 while not appreciably oxidizing M2 is that reaction (1) is favored as compared to reaction (2). In other words, E1 is less than E2. In the case where M1 represents silicon, polycrystalline silicon, or amorphous silicon and M2 represents tungsten,
Si + O2 → SiO2 - 911 kJ/mol (3)
(2/3)W + O2 → (2/3)WO3 -562 kJ/mol (4)
Hence, since E1 is less than E2 (-911 kJ/mol versus -562 kJ/mol), the silicon of reaction (3) will oxidize much more readily than the tungsten of reaction (4). - A method of fabricating a capacitor having a dielectric between a bottom electrode and a top electrode and situated over a semiconductor substrate is provided. The method comprises the steps of: providing the bottom electrode over the semiconductor substrate; providing an oxidizable dielectric material over the bottom electrode; and subjecting the bottom electrode and the oxidizable dielectric material to an explosive reaction between O2 and H2 in a semiconductor processing chamber, wherein the oxidizable dielectric material is oxidized and the bottom electrode remains substantially unoxidized, such that the reaction between the O2 and H2 does not increase the pressure in the processing chamber beyond a predetermined safe level. The dielectric material is, preferably, comprised of a material selected from the group consisting of: an oxide/nitride stack, BST, tantalum pentoxide, PZT, or any combination thereof.
- The present invention will now be further described, by way of example, with reference to the accompanying drawings in which:
-
FIGURE 1 is cross-sectional view of a device formed using a method of fabrication; -
FIGURE 2 is a TEM photograph of devices formed using the method of fabrication; -
FIGURE 3 is a cross-sectional view of a memory cell formed using the method of an alternative method of fabricating and; -
FIGURE 4 is a graph illustrating the sheet resistivity of a Tungsten layer. - A method of oxidizing selective materials such as silicon (single crystal, polycrystalline, or amorphous silicon) without appreciably oxidizing any other materials (such as a tungsten or tungsten nitride structure) is disclosed herein. In one embodiment the oxidation is performed by introducing hydrogen gas and oxygen gas into a chamber where the semiconductor wafer resides and heating the wafer and/or the chamber. Note, however, that the introduction of hydrogen gas along with oxygen gas can be very volatile.
- In order to safely oxidize the desired structure while leaving other structures (preferably the refractory metals) unoxidized using oxygen and hydrogen gases, the system pressure should not exceed its safety limit in the presence of the following reaction
2H2 + O2 → 2 H2O + E (5)
where E is the enthalpy generated by this reaction. - If the system/chamber is first filled with H2 and O2 before reaction (5) takes place, then the final pressure of the system is given by:
where T = E/(heat capacitance of the resulting gas system), P is the ending pressure, P0 is the starting pressure of the system, T0 is the starting temperature, and the heat capacitance is a function of the O2 to H2 ratio (and assuming it is independent of the temperature). For example, starting at 500°C with a constant volume mix of O2 in H2 (ratio of 1:10) and an initial pressure of 200 Torr (1 Torr = 133 Pa), the final pressure of the system (using equation (1)) is about 600 Torr which is less than the pressure of the atmosphere. Therefore, this process should be safe. - If reaction (5) occurs as H2 and O2 are entered into the system, then the reaction occurs in only part of the volume of the chamber. By doing this, the safety of the process is improved and the process window can be enlarged because the reaction occurs in only a portion of the total volume of the process chamber thereby leaving the rest of the volume available for expansion. In this case, reaction (5) occurs continuously as the gases enter into the chamber instead of filling the entire chamber with the gases before ignition of the gases.
- A variation of this approach is to start the reaction at a lower pressure and increase the pressure once the reaction starts. Anther variation involves starting the reaction at a lower concentration of one gas (such as O2) and increasing the concentration once the reaction starts.
-
FIGUREs 1 and2 illustrate a transistor formed using such a method. After gate insulating layer 104 (preferably an oxide layer -- more preferably SiO2) is formed, a semiconductive layer (preferably insitu doped, exsitu doped, or undoped polysilicon) is formed (preferably deposited by chemical vapor deposition). Next, a metal layer is formed (preferably deposited). Preferably, the metal layer is comprised of a refractory metal (preferably tungsten, cobalt, aluminum, or titanium) formed over a nitride layer (preferably comprised of the refractory metal and nitrogen -- more preferably tungsten nitride). This is followed by the formation of a nitride layer (preferably comprised of silicon and nitride - more preferably Si4N3). - Next, these layers are etched to form gate structure 120 (preferably comprised of
polysilicon structure 108,tungsten nitride structure 110,tungsten structure 112, and silicon nitride structure 114). Preferably, this etch step is performed by reactive ion etch (RIE) but it can be accomplished using any standard processing step. One drawback to this etch step, especially when RIE is used, is that it may degrade the gate dielectric atlocations 106. If left untreated, this may increase the leakage of the device or may lower the gate oxide integrity (GOI) thereby rendering the device non-functional or damaged. Using conventional oxidation methods, the damaged portions ofgate insulating layer 104 are reoxided along with the oxidation ofsurfaces 116 ofpolysilicon structure 108 andsurfaces 118 ofmetal structure metal structures layers 110 and 112) may greatly decrease due to the oxidation of the metal (especially where the metal is tungsten). Oxidation ofmetal structures layer 104 and the oxidation of silicon-containingstructure 108 while leaving metal structure 112 (preferably comprised of W, Ti, Co, Cu, or Al) and metal-nitride structure 110 (preferably comprised of a nitride and a refractory metal such as W, Ti, Co, Cu, or Al - more preferably tungsten nitride) substantially unoxidized. This is shown inFIGURE 2 whereregion 208 is equivalent toregion 108, region 210 is equivalent toregions region 214 is equivalent toregion 114 andregion 216 illustrates the formed oxide regions on the side ofregion 208. - In a method of fabrication, this oxidation step is accomplished by providing around 12% O2 and H2 into a chamber in which the wafer is provided. The pressure within the chamber is preferably around 100 Torr and the temperature is around 1000°C. Using this embodiment for around 60 to 80 seconds (preferably 70 seconds) will result in around 3 nm of oxide to be formed on bare silicon and thin silicon oxide, and it will result in around 6 to 10 nm of oxide to be grown on polysilicon structures. While these specific conditions are preferred, the temperature, pressure, time, and amount of oxygen versus that of hydrogen can be changed so as to grow more or less of an oxide film so long as oxidation of the silicon or silicon oxide structure is accomplished while not substantially oxidizing the metal or metal nitride structures.
- This method of fabrication may be implemented to selectively oxidize silicon structures in the presence of tungsten under the following conditions: the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O2 to H2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours.
- In an alternative method of fabrication, the mixture of hydrogen and oxygen can be used to selectively oxidize a particular material (such as Ta2O5 or BST) without oxidizing other materials which are present (such as copper, tungsten, platinum, or other refractory metal or conductive structure which may be used to make an electrode of a memory cell) in developing electronic devices (such as the memory cell of a DRAM). This particular selective oxidation method can be accomplished by using an O2 and H2 ambient to oxidize a capacitor dielectric. While this alternative method is preferably performed as a rapid thermal process step with relatively low ambient pressures, it can be implemented in many ways. An advantage of this method is that it may be implemented using a lower thermal budget (preferably, the temperatures required will be around 400 to 1000°C) and it can be used so as to oxidize the capacitor dielectric while leaving other features (such as tungsten, platinum, copper, or other similar materials) substantially unoxidized.
- Preferably, this alternative method of fabrication may be implemented under the following conditions: the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O2 to H2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours.
-
FIGURE 3 illustrates a memory cell which is fabricated using the method disclosed herein. The memory cell can be formed either over or under the bitline, and it may either be formed as a "crown cell" or as a planar cell and it may or may not be formed of rugged polysilicon or hemispherical grain polysilicon. The memory cell ofFIGURE 3 is comprised ofsubstrate 302,interlevel dielectric 304, conductive plug 306 (preferably comprised of doped single-crystal or polycrystalline silicon),bottom electrode base 310 andupright portions 312,dielectric layer 314 andtop electrode 316. Basically, the method can be used to either form dielectric 314 and/or to prevent the oxidation ofbottom electrode conductive plug 306 andelectrode - An alternative method of fabrication can be used to form the
capacitor dielectric 314 or to reoxidize capacitor dielectric so as to enhance it properties. Preferably, dielectric 314 is formed or reoxided by subjecting the wafer to a mixture of H2 and O2. Preferably, this is accomplished using the following conditions: the ambient temperature is between 300 and 1200°C; the pressure is around 1 Torr to 10 atmospheric pressure; the oxidizer to reducer ratio, O2 to H2 ratio, respectively, is around 0.1% to 99.9%; and the duration is around 1 second to 10 hours. -
FIGURE 4 is a graph illustrating relative sheet resistivity of a tungsten layer which is approximately 60 nm thick and is subjected to the oxidation step of the method disclosed herein versus the percentage of O2/H2 mixture. The pressure is around 100 Torr at around 1000°C. Points Point 406 illustrates that the sheet resistivity of a tungsten layer subjected to an oxidation step of the instant invention, where the O2/H2 mixture is around 20%, has a sheet resistivity around 20% higher than that of an untreated tungsten layer.
Claims (2)
- A method of fabricating, in a semiconductor processing chamber, a capacitor having a dielectric between a bottom electrode and a top electrode and situated over a semiconductor substrate, said method comprising the steps of:providing said bottom electrode over said semiconductor substrate;providing an oxidizable dielectric material over said bottom electrode; andsubjecting said bottom electrode and said oxidizable dielectric material to a reaction between O2 and H2 in the semiconductor processing chamber, wherein said oxidizable dielectric material is oxidized and said bottom electrode remains substantially unoxidized, such that the reaction between said O2 and H2 does not increase the pressure in the processing chamber beyond a predetermined safe level.
- The method of Claim 1, wherein said step of providing an oxidizable dielectric material comprises providing a dielectric material selected from the group consisting of: an oxide/nitride stack, BST, tantalum pentoxide, PZT, or any combination thereof.
Priority Applications (1)
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EP09153586.4A EP2063464B1 (en) | 1997-10-14 | 1998-10-13 | Method for oxidizing a structure during the fabrication of a semiconductor device |
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US6182797P | 1997-10-14 | 1997-10-14 | |
US61827P | 1997-10-14 |
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EP09153586.4A Division EP2063464B1 (en) | 1997-10-14 | 1998-10-13 | Method for oxidizing a structure during the fabrication of a semiconductor device |
Publications (3)
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EP0910119A2 EP0910119A2 (en) | 1999-04-21 |
EP0910119A3 EP0910119A3 (en) | 2001-02-07 |
EP0910119B1 true EP0910119B1 (en) | 2009-06-03 |
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EP09153586.4A Expired - Lifetime EP2063464B1 (en) | 1997-10-14 | 1998-10-13 | Method for oxidizing a structure during the fabrication of a semiconductor device |
EP98308341A Expired - Lifetime EP0910119B1 (en) | 1997-10-14 | 1998-10-13 | Method for oxidizing a structure during the fabrication of a semiconductor device |
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EP09153586.4A Expired - Lifetime EP2063464B1 (en) | 1997-10-14 | 1998-10-13 | Method for oxidizing a structure during the fabrication of a semiconductor device |
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EP (2) | EP2063464B1 (en) |
JP (1) | JPH11238702A (en) |
DE (1) | DE69840861D1 (en) |
Families Citing this family (5)
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US6534401B2 (en) * | 2000-04-27 | 2003-03-18 | Applied Materials, Inc. | Method for selectively oxidizing a silicon/metal composite film stack |
JP4801248B2 (en) * | 2000-10-31 | 2011-10-26 | アプライド マテリアルズ インコーポレイテッド | Oxide film forming method and apparatus |
US6638877B2 (en) * | 2000-11-03 | 2003-10-28 | Texas Instruments Incorporated | Ultra-thin SiO2using N2O as the oxidant |
JP4706260B2 (en) * | 2004-02-25 | 2011-06-22 | 東京エレクトロン株式会社 | Process for oxidizing object, oxidation apparatus and storage medium |
US7951728B2 (en) * | 2007-09-24 | 2011-05-31 | Applied Materials, Inc. | Method of improving oxide growth rate of selective oxidation processes |
Citations (1)
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US5257926A (en) * | 1991-12-17 | 1993-11-02 | Gideon Drimer | Fast, safe, pyrogenic external torch assembly |
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JPS59132136A (en) * | 1983-01-19 | 1984-07-30 | Hitachi Ltd | Manufacture of semiconductor device |
JPS609166A (en) * | 1983-06-29 | 1985-01-18 | Hitachi Ltd | Manufacture of semiconductor device |
JPS60134441A (en) * | 1983-12-23 | 1985-07-17 | Hitachi Ltd | Semiconductor device |
JPS60250630A (en) * | 1984-05-28 | 1985-12-11 | Hitachi Ltd | Manufacture of semiconductor device |
JPH04328862A (en) * | 1991-04-30 | 1992-11-17 | Hitachi Ltd | Manufacture of semiconductor integrated circuit device |
JP3207943B2 (en) * | 1992-11-17 | 2001-09-10 | 忠弘 大見 | Low temperature oxide film forming apparatus and low temperature oxide film forming method |
JPH0766408A (en) * | 1993-08-31 | 1995-03-10 | Toshiba Corp | Manufacture of semiconductor device |
-
1998
- 1998-10-13 EP EP09153586.4A patent/EP2063464B1/en not_active Expired - Lifetime
- 1998-10-13 DE DE69840861T patent/DE69840861D1/en not_active Expired - Lifetime
- 1998-10-13 EP EP98308341A patent/EP0910119B1/en not_active Expired - Lifetime
- 1998-10-14 JP JP10292302A patent/JPH11238702A/en active Pending
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US5257926A (en) * | 1991-12-17 | 1993-11-02 | Gideon Drimer | Fast, safe, pyrogenic external torch assembly |
Also Published As
Publication number | Publication date |
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EP2063464B1 (en) | 2017-11-29 |
EP2063464A3 (en) | 2009-06-17 |
EP2063464A2 (en) | 2009-05-27 |
JPH11238702A (en) | 1999-08-31 |
EP0910119A3 (en) | 2001-02-07 |
EP0910119A2 (en) | 1999-04-21 |
DE69840861D1 (en) | 2009-07-16 |
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